Cryogenic systems which provide power to pneumatically operated tools are known. Such tools may include nail drivers, screwdrivers, chisels, impact wrenches and the like. Cryogenic systems that provide oxygen supplementation for persons having restricted breathing ability are also known. Examples of such prior systems are disclosed in U.S. Pat. Nos. 4,149,388 and 4,211,086, respectively.
An important aspect for any pneumatic power source is that it must be mobile, preferably even portable, to provide driving power at the location at which the pneumatic tool is being used. At such locations it is often impractical to utilize a bulky air compressor or a heavy pressurized-gas vessel. Each of these characteristics impairs the portability of the power source; thus, a desirable power source is portable and light-weight.
Another important aspect of such a power source is ruggedness. Often the power source is used at a construction site or transported in or on the flatbed of a vehicle, such as the well of a pickup truck. The equipment is often handled roughly by those operating the equipment, and it must be able to withstand such treatment and be reliable on the job. Even a brief malfunction or breakdown of the equipment can prove costly.
One prior pneumatic power source, as disclosed in U.S. Pat. No. 4,149,388, comprises a portable cryogenic system for powering small pneumatic hand tools comprising a small dewar for storing liquid cryogen provided with an inner vessel and an outer vessel, each having a central opening at its upper portion, and an insulative layer in the volume between the inner and outer vessels. The inner vessel and outer vessel are connected in a sealing engagement by a neck portion at the central openings of each vessel. The neck portion is rigid and provides little, if any, flexibility of the inner vessel. During rough field use, the inflexibility of the neck portion may result in the breaking of the sealing engagement between the inner and outer vessels, thereby destroying the vacuum capability of the volume between the vessels, substantially diminishing the dewar's ability to store cryogenic liquid for substantial periods, and resulting in a substantially dimished useability of the power system.
The prior system was pressurized by tipping the dewar so that the cryogenic liquid stored in the inner vessel contacted the exposed portion of the bottom surface of a fluid manifold secured to the upper end of the dewar so that the cryogenic fluid was exposed to a substantial heat transfer from the ambient exterior environment. The thermal contact resulted in vaporization of a portion of the cryogenic liquid which increased the pressure within the vessel until the predetermined operating pressure is reached. The system generally operated in the pressure range from about 90 to 110 pounds per square inch (psi), and once the operable pressure was reached, a pneumatic tool could then be connected to the power source to provide the flow of pressurized gas to drive the tool. Such a procedure to build pressure was slow and required interruption in the use of the power source to build a useable pressure. In addition, in many situations, such as a worker standing on a ladder, it is impractical to have to continuously tip the dewar to maintain the operating pressure within the system.
Cryogenic breathing systems for providing supplementary oxygen to people having restricted breathing ability are also known, for example, from U.S. Pat. No. 4,211,086. This system includes a storage container for liquid oxygen and a portable container for liquid oxygen, the portable container being refillable from the stationary storage container, both containers being able to provide oxygen for breathing. Each container includes a rigid outer casing having a small opening in its top as well as an inner container having a corresponding small opening at its top. The openings of the outer casing and of the inner container are connected together by a gas-tight tubular connection forming an evacuable space between the outer casing and the inner container. The system was adapted to provide a flow of oxygen at low pressures on the order of 20 psi for breathing purposes and was not able to provide highly pressurized gas for operating pneumatic tools.
A portable system for powering pneumatic tools must be capable of withstanding the relatively high pressures needed to operate most pneumatic tools; the physical size of the container must be small enough to be of a practical and usable size; and the system should be capable of providing a continuous flow of gas at high pressure for extended practical periods of time. Such containers must be constructed in such a manner that they can pass A.S.M.E. standards for pressure vessels. The pressures under which the gas is stored are generally higher than that needed to operate pneumatic tools, which are commonly designed to operate at a pressure level of about 50 to about 80 psi. Thus, a pressure regulator is generally coupled with the power source tool to control the pressure of the gas being delivered to the tool. Gases stored at such high pressures may be dangerous if not stored and handled properly, and pressure control and relief systems are desirable to prevent damage and injury during use of such portable containers. Efforts in the past to devise a portable, pneumatic power source having the desirable characteristics discussed above have not been successful to date.